1. Field of the Invention
The present invention relates to a process for producing a highly purified sweet steviol glycoside mixture, Stevioside and Rebaudioside A from the extract of the Stevia rebaudiana Bertoni plant and use thereof in various food products and beverages.
2. Description of the Related Art
In view of food sanitation, the use of artificial sweeteners such as dulcin, sodium cyclamate and saccharin has been restricted. However natural sweeteners have been receiving increasing demand. Stevia rebaudiana Bertoni is a plant that produces an alternative sweetener that has an added advantage of being a natural plant product. In addition, the sweet steviol glycosides have functional and sensory properties superior to those of many high potency sweeteners.
The extract of Stevia rebaudiana plant contains a mixture of different sweet diterpene glycosides, which have a single base—steviol and differ by the presence of carbohydrate residues at positions C13 and C19. These glycosides accumulate in Stevia leaves and compose approximately 10%-20% of the total dry weight. Typically, on a dry weight basis, the four major glycosides found in the leaves of Stevia are Dulcoside A (0.3%), Rebaudioside C (0.6%), Rebaudioside A (3.8%) and Stevioside (9.1%). Other glycosides identified in Stevia extract include Rebaudioside B, C, D, E, and F, Steviolbioside and Rubusoside.
The physical and sensory properties are well studied only for Stevioside and Rebaudioside A. They were tested for stability in carbonated beverages and found to be both heat and pH stable (Chang and Cook, 1983). The sweetness potency of Stevioside is around 210 times higher than sucrose, Rebaudioside A in between 200 and 400 times, and Rebaudioside C and Dulcoside A around 30 times (Phillips, 1989 and Tanaka, 1997).
However, apart from its high level of sweetness, they have also intrinsic properties of post-bitter taste and unpleasant and undesirable aftertaste. Some undesirable taste characteristics of glycosides can be as a result of contamination of other substances, presented in extract.
One of the main ways to improve the taste quality is the enzymatic glycosylation of mixture of semi-purified steviol glycosides. Another way is to produce highly purified individual glycosides with standard characteristics and minimal content of accompanying compounds.
The invention related to the purification of two main glycosides—Stevioside and Rebaudioside A and use thereof.
A process for the recovery of diterpene glycosides, including Stevioside from the Stevia rebaudiana plant is described (U.S. Pat. No. 4,361,697). A variety of solvents, having different polarities, were used in a sequential treatment that concluded with a high performance liquid chromatographic (HPLC) separation procedure.
A method for the recovery of Rebaudioside A from the leaves of Stevia rebaudiana plants has been developed (U.S. Pat. No. 4,082,858). Again, final purification is achieved by liquid chromatography subsequent to an initial extraction with water and an alkanol having from 1 to 3 carbon carbons, preferably methanol. It is also known that water may be used as the initial solvent; their preferred solvent at this stage is a liquid haloalkane having from 1 to 4 carbon atoms. The preferred second solvent is an alkanol having from 1 to 3 carbon atoms, while the preferred third solvent is an alkanol having from 1 to 4 carbon atoms and optionally minor amounts of water.
Individual sweet glycosides can be obtained from the Stevia rebaudiana plant. A mixture of sweet glycosides extracted from the Stevia rebaudiana plant is processed to remove impurities by using two types of ion-exchangers. After removing the mixed sweet glycosides from the second column with methanol, the solution is dried. Upon refluxing the dried solids in a methanol solution and then cooling the solution, Stevioside precipitates out. The filtrate is further concentrated and cooled to precipitate out Rebaudioside A. This Rebaudioside A can be further purified as can the previously obtained Stevioside (U.S. Pat. No. 5,962,678). However, a large amount of toxic organic solvent, such as methanol is used.
However, all the above-mentioned methods allow the production of Stevioside and Rebaudioside A not in highly purified grade, which further possess a residual bitterness and aftertaste.
On the other hand, the unfavorable taste of the glycosides can be as a result of contamination of impurities, presented in extract. Highly purified Stevioside and Rebaudioside A possessing an improved taste profile and there is a need to provide an easy and commercially valuable process for the manufacturing the highly purified Stevioside and Rebaudioside A, and use thereof in various beverages and food products.